Germination parameters of neotropical forest and savanna species.
Description
Models predicting the distribution of savannas worldwide have identified rainfall and fire as their primary determinants. However, most of them have relied upon adult traits, while juvenile traits, at the bottleneck of the plant's life cycle, have been largely overlooked. We developed a novel mechanistic model based on the effects of temperature and fire on germination traits to predict the distribution of Cerrado, i.e., the largest neotropical savanna. We compiled data on the germination of seeds subjected to temperature and heat shock treatments and used generalized additive mixed models to predict germination potential as a function of temperature, species, physiognomy (forest/savanna). The best model showed that seasonal temperatures set the germination limits for seeds of both savanna and forest physiognomies. Forest seeds presented a higher germinability in the optimum temperature range, but savanna seeds had higher survival rates after heat shocks. The model revealed that the southern limit of Cerrado is determined by low winter temperatures, while the western and eastern boundaries are set by high summer temperatures. The model also predicted an area of high germination potential that coincides with high biodiversity and climate stability in the Cerrado. We showed that germination traits are highly valuable to predict vegetation responses to climate. Seasonal temperatures are primary determinants of the Cerrado’s extent, while fire favors the recruitment of savanna species over the Cerrado–Amazonia ecotone. Global warming may significantly impact the germination potential of native species. This data was used to model the impacts of climate on current and future distribution of the Cerrado biome and published at the Journal of Vegetation Science (DOI 10.1111/jvs.12988).
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An exhaustive survey of the published literature was conducted to raise data on morphology and germination parameters of seeds subjected to temperature and heat shock treatments. We considered only studies conducted with species native of the Cerrado biome, as well with species native from other biomes but frequent and widely distributed over the Cerrado. We assembled from literature data on a total of 170 species (Datasets attached). To check for data consistency, we produced a preliminary map of missingness with the missmap function of package AmeliA. This approach revealed that the variables SD of germinability, SD of germination time and time of seed dispersal had insufficient data for analysis, so we dropped them. As the variables germination time and seed dry mass were robust, although still incomplete, we ran the function complete of the mice package to impute missing values before proceeding with model selection. We assessed the effects of the predictors family, habit, physiognomy, seed dry mass, germinability, and germination time on germination potential. Because there are repeated measurements of germinability and germination time for each species, taken at different temperatures and different sites, we used the uGamm function of package mgcv to predict germination potential over a temperature gradient. We built two models, one for germinability and another for germination time. In each model, we used site nested within species as the random effect; dry mass, physiognomy, family, and habit as fixed effects; and temperature as smooth effect. We performed model selection with the dredge function of package mumin to assess the importance of fixed effects and choose a single best model for inference and prediction. We estimated TPCs with the function get_predict of pack- age mApinguAri (Caetano et al., 2020). After preliminary tests (Appendix S2b), we estimated TPCs by habit (herb/shrub/trees) and physiognomy (rocky field/forest/savanna), for comparisons and to predict temperature effects on germination at the community level. We modeled temperature effects on germinability in the interval 5–50°C, which permitted us to set minimum (CTmin), optimum (Topt), and maximum (CTmax) germination temperatures by species, also ex- trapolating to physiognomies and habits. We assessed data from the literature on the effects of heat shocks (simulating fire) on the germinability and germination time of seeds impacts on vegetation distribution, we used the Physical Chemistry. Several ecological information as dispersal time and mode, habits, physiognomy of occurrence and other information are also provided. This data was used to model the impacts of climate on current and future distribution of the Cerrado biome and published at the Journal of Vegetation Science (DOI 10.1111/jvs.12988).